Signaling for proximity services and d2d discovery in an lte network

ABSTRACT

Embodiments of an enhanced node B (eNB), user equipment (UE) and methods of signaling for proximity services and device-to-device (D2D) discovery in an LTE network are generally described herein. In some embodiments, the eNB may transmit signaling to indicate D2D discovery zone configuration to proximity service (ProSe) enabled UEs. The signaling may indicate time and frequency resources and a periodicity of a discovery zone and may indicate operational parameters for the discovery zone. The resources of the D2D discovery zone may be allocated for D2D discovery signal transmission by the ProSe-enabled UEs.

PRIORITY CLAIMS

This application claims the benefit of priority under 35 USC 119(e) toU.S. Provisional Patent Application Ser. No. 61/863,902, filed Aug. 8,2013 [reference number 4884.080PRV P60233Z], and U.S. Provisional PatentApplication Ser. No. 61/909,938, filed Nov. 27, 2013 [reference number884.Q84PRV P62670Z], each of which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless communications. Some embodiments relateto 3GPP LTE (Long Term Evolution) networks. Some embodiments relate todirect device-to-device (D2D) communication. Some embodiments relate todevice discovery in LTE networks.

BACKGROUND

Proximity-based applications and services represent a fast growingsocial and technological trend that may have a major impact on evolutionof cellular wireless/mobile broadband technologies. These services arebased on the awareness of two devices or two users being close to eachother and may include such applications as public safety operations,social networking, mobile commerce, advertisement, gaming, etc. Deviceto device (D2D) discovery is the first step to enable D2D service. Withdirect D2D communication, user equipment (UE) may communicate directlywith each other without involvement of a base station or an enhancednode B (eNB). One issue with D2D communication is device discovery toenable D2D service. Device discovery involves discovering one or moreother discoverable UEs within communication range for D2D communication.Device discovery also involves being discovered by one or more otherdiscovering UEs within communication range for D2D communication. Thereare many unresolved issues with respect to device discovery for D2Dcommunication including resource allocation and signaling, particularlyfor Proximity Service (ProSe) D2D discovery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a portion of an end-to-end network architecture of an LTEnetwork in accordance with some embodiments;

FIG. 2 shows a structure for a resource grid including a discovery zonefor D2D communications in accordance with some embodiments;

FIG. 3A illustrates the reporting of discovery zone metrics inaccordance with some embodiments;

FIG. 3B illustrates the use of a random-access channel (RACH) to countProSe-enabled UEs in accordance with some embodiments;

FIG. 4 illustrates a procedure for counting ProSe-enabled UEs for UEs inradio-resource control (RRC) connected mode;

FIG. 5 illustrates cooperative uplink subframe power control for D2Ddiscovery signal transmission in accordance with some embodiments;

FIG. 6 illustrated eNB-triggered contention-free D2D discovery zoneresources in accordance with some embodiments;

FIG. 7 illustrated UE-triggered contention-free D2D discovery zoneresources in accordance with some embodiments; and

FIG. 8 illustrates a functional block diagram of a wirelesscommunication device in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

Embodiments disclosed herein provide signaling designs for the supportof LTE Proximity Services (ProSe) D2D discovery. In these embodiments,UEs may be ProSe-enabled UEs configured for D2D discovery signaltransmission and D2D communication. Some embodiments provideconfiguration of D2D discovery zones with partitioning of D2D DiscoveryZones into contention-based and non-contention-based Discovery Zones forboth network-common and cell-specific configurations of discovery zones.Some embodiments provide mechanisms for UE feedback to provide an eNBwith information about the loading of discovery zones. Some embodimentsprovide options for support of inter-cell/eNB discovery. Someembodiments provide for the use and configuration of silencing factorsfor random silencing/adaptive random silencing for transmission of D2Ddiscovery packets. Some embodiments provide for signaling contents thatinclude: the discovery zone configuration, a silencing factor, atransmit power control configuration, hopping related parameters, and ascrambling identity for scrambling of cyclic-redundancy check (CRC) maskof discovery packets. Some embodiments provide signaling mechanisms forthe above-mentioned signaling contents. Some embodiments provide forstatic provisioning and/or pre-configuration of D2D discovery resources.Some embodiments provide for network and UE behavior to supportcontention-free direct device discovery. These embodiments are discussedin more detail below.

FIG. 1 shows a portion of an end-to-end network architecture of an LTEnetwork with various components of the network in accordance with someembodiments. The network 100 comprises a radio access network (RAN)(e.g., as depicted, the E-UTRAN or evolved universal terrestrial radioaccess network) 100 and the core network 120 (e.g., shown as an evolvedpacket core (EPC)) coupled together through an S1 interface 115. Forconvenience and brevity sake, only a portion of the core network 120, aswell as the RAN 100, is shown.

The core network 120 includes mobility management entity (MME) 122,serving gateway (serving GW) 124, and packet data network gateway (PDNGW) 126. The RAN includes enhanced node B's (eNBs) 104 (which mayoperate as base stations) for communicating with user equipment (UE)102. The eNBs 104 may include macro eNBs and low power (LP) eNBs. UEs102 may be ProSe-enabled.

The MME is similar in function to the control plane of legacy ServingGPRS Support Nodes (SGSN). The MME manages mobility aspects in accesssuch as gateway selection and tracking area list management. The servingGW 124 terminates the interface toward the RAN 100, and routes datapackets between the RAN 100 and the core network 120. In addition, itmay be a local mobility anchor point for inter-eNB handovers and alsomay provide an anchor for inter-3GPP mobility. Other responsibilitiesmay include lawful intercept, charging, and some policy enforcement. Theserving GW 124 and the MME 122 may be implemented in one physical nodeor separate physical nodes. The PDN GW 126 terminates an SGi interfacetoward the packet data network (PDN). The PDN GW 126 routes data packetsbetween the EPC 120 and the external PDN, and may be a key node forpolicy enforcement and charging data collection. It may also provide ananchor point for mobility with non-LTE accesses. The external PDN may beany kind of IP network, as well as an IP Multimedia Subsystem (IMS)domain. The PDN GW 126 and the serving GW 124 may be implemented in onephysical node or separated physical nodes.

The eNBs 104 (macro and micro) terminate the air interface protocol andmay be the first point of contact for a UE 102. In some embodiments, aneNB 104 may fulfill various logical functions for the RAN 100 includingbut not limited to RNC (radio network controller functions) such asradio bearer management, uplink and downlink dynamic radio resourcemanagement and data packet scheduling, and mobility management.

The S1 interface 115 is the interface that separates the RAN 100 and theEPC 120. It is split into two parts: the S1-U, which carries trafficdata between the eNBs 104 and the serving GW 124, and the S1-MME, whichis a signaling interface between the eNBs 104 and the MME 122. The X2interface is the interface between eNBs 104. The X2 interface comprisestwo parts, the X2-C and X2-U. The X2-C is the control plane interfacebetween the eNBs 104, while the X2-U is the user plane interface betweenthe eNBs 104.

With cellular networks, LP cells are typically used to extend coverageto indoor areas where outdoor signals do not reach well, or to addnetwork capacity in areas with very dense phone usage, such as trainstations. As used herein, the term low power (LP) eNB refers to anysuitable relatively low power eNB for implementing a narrower cell(narrower than a macro cell) such as a femtocell, a picocell, or a microcell. Femtocell eNBs are typically provided by a mobile network operatorto its residential or enterprise customers. A femtocell is typically thesize of a residential gateway or smaller and generally connects to theuser's broadband line. Once plugged in, the femtocell connects to themobile operator's mobile network and provides extra coverage in a rangeof typically 30 to 50 meters for residential femtocells. Thus, a LP eNBmight be a femtocell eNB since it is coupled through the PDN GW 126.Similarly, a picocell is a wireless communication system typicallycovering a small area, such as in-building (offices, shopping malls,train stations, etc.), or more recently in-aircraft. A picocell eNB cangenerally connect through the X2 link to another eNB such as a macro eNBthrough its base station controller (BSC) functionality. Thus, LP eNBmay be implemented with a picocell eNB since it is coupled to a macroeNB via an X2 interface. Picocell eNBs or other LP eNBs may incorporatesome or all functionality of a macro eNB. In some cases, this may bereferred to as an access point base station or enterprise femtocell.

In some LTE embodiments, a physical downlink shared channel (PDSCH)carries user data and higher-layer signaling to a UE 102. The physicaldownlink control channel (PDCCH) carries information about the transportformat and resource allocations related to the PDSCH channel, amongother things. It also informs the UE 102 about the transport format,resource allocation, and H-ARQ information related to the uplink sharedchannel. Typically, downlink scheduling (assigning control and sharedchannel resource blocks to UEs within a cell) is performed at the eNB104 based on channel quality information fed back from the UEs 102 tothe eNB 104, and then the downlink resource assignment information issent to a UE on a physical downlink control channel (PDCCH) used for(and possibly assigned to) the UE 102.

The PDCCH uses CCEs (control channel elements) to convey the controlinformation. Before being mapped to resource elements, the PDCCHcomplex-valued symbols may be first organized into quadruplets, whichare then permuted using a sub-block inter-leaver for rate matching. EachPDCCH is transmitted using one or more of these control channel elements(CCEs), where each CCE corresponds to nine sets of four physicalresource elements known as resource element groups (REGs). Four QPSKsymbols are mapped to each REG. The PDCCH may be transmitted using oneor more CCEs, depending on the size of DCI and the channel condition.There may be four or more different PDCCH formats defined in LTE withdifferent numbers of CCEs (e.g., aggregation level, L=1, 2, 4, or 8).

In accordance with some embodiments, the UEs 102 that are ProSe-enabledmay be arranged for device-to-device (D2D) communications including D2Ddiscovery of other UEs 102 for direct D2D communication. In theseembodiments, ProSe-enabled UEs 102 may transmit discovery signals 101within discovery resources to discover one or more other ProSe-enabledUEs. These embodiments are discussed in more detail below.

FIG. 2 shows a structure for a resource grid including a discovery zonefor D2D communications in accordance with some embodiments. The depictedgrid is a time-frequency grid, called a resource grid, which is thephysical resource in the downlink or uplink in each slot. The smallesttime-frequency unit in a resource grid is denoted as a resource element(RE). The resource grid comprises a number of resource blocks (RBs)which describe the mapping of certain physical channels to resourceelements. Each resource block comprises a collection of resourceelements and in the frequency domain, represents the smallest quanta ofresources that may be allocated, although the scope of the embodimentsis not limited in this respect. There are several different physicalchannels that are conveyed using such resource blocks. The resource gridillustrated in FIG. 2 may comprise an LTE operation zone 202 which maycomprise a plurality of physical RBs (PRBs) for use by the RAN 100.

In accordance with some embodiments, a UE 102 (FIG. 1) may receivesignaling from an eNB 104 (FIG. 1) indicating a discovery zone 204within the LTE operation zone 202. The discovery zone 204 may comprise aplurality of PRBs 206 of a discovery resource. The UE 102 may transmit adiscovery signal or discovery packet 101 (FIG. 1) for receipt by one ormore other UEs for D2D discovery within some PRBs 206 of the discoveryzone 204. In some embodiments, the resources allocated for D2D discoverymay be resources of a physical-uplink shared channel (PUSCH), althoughthe scope of the embodiments is not limited in this respect.

A PRB may be associated with a particular slot of a subframe in the timedimension and a particular group of frequency subcarriers in thefrequency dimension. Each PRB, for example, may be identified by a RBindex and a subframe index. In some embodiments, a discovery packet 101may be transmitted within M subframes of N resources blocks where M andN are at least one and may be greater than one. These embodiments aredescribed in more detail below.

In some embodiments, a PRB may comprise twelve sub-carriers in thefrequency domain by 0.5 ms (i.e., one slot) in the time domain. The PRBsmay be allocated in pairs (in the time domain), although this is not arequirement. In some embodiments, a PRB may comprise a plurality of REs.A RE may comprise one sub-carrier by one symbol. When a normal CP isused, a RB contains seven symbols. When an extended CP is used, the RBcontains six symbols. A delay spread that exceeds the normal CP lengthindicates the use of extended CP. Each subframe may be one millisecond(ms) and one frame may comprise ten such subframes.

There are two different approaches in D2D discovery: restricted/closedD2D discovery and open D2D discovery. Restricted/closed D2D discoveryapplies to use cases wherein a discoverable device may be discoveredonly by a select set of ProSe-enabled discovering devices. A furtherimplication of closed device discovery is consideration of scenarioswherein a discovering device tries to discover particular ProSe-enableddevice(s) (one or many from a set of ProSe-enabled devices). Thus, forthis use case, a discovering device would be assumed to know theProSe-enabled device it wishes to discover in its proximity.

Contrary to closed D2D discovery, open device discovery considers usecases wherein a discoverable device may want itself to be discovered byother ProSe-enabled devices in its proximity. From the perspective ofthe discovering device, open device discovery implies that a discoveringdevice may not be assumed to be aware of the identity of otherProSe-enabled devices prior to discovery. Consequently, the devicediscovery mechanism for open discovery should aim towards discovering asmany ProSe-enabled devices in its proximity as possible.

For open D2D discovery, an eNB 104 has limited control on the discoveryprocess among UEs 102. In particular, an eNB 104 may periodicallyallocate certain discovery resources in the form of D2D discoveryregions for a UE 102 to transmit the discovery information. Thediscovery information may be in the form of discovery sequence ordiscovery packet with payload information. The discovery relatedinformation content that UEs intend to share with each other may behigher as the design would need to transmit the unique ID for deviceidentification, service identity, etc. (e.g., 48 bits or more) as datapayload, protected by CRC. The number of resource blocks (RB) requiredfor discovery packet transmission in open D2D discovery design, which isdenoted as L_(RB) ^(D2D), may be 1 or more, depending on the payloadsize and the overall discovery performance requirement.

In some embodiments, a discovery region may comprise a number ofoccurrences of periodic discovery zones, with each discovery zonecomprising of some RBs in frequency domain and several subframes in timedomain. FIG. 2 shows an example of a discovery zone 204 within LTEoperation zone 202 in which, N_(RB) ^(D2D), n_(RB) ^(start), N_(SF)^(D2D) and n_(SF) ^(start) are denoted as the number of allocated RBs,the starting RB index and the number of subframes, the starting subframeindex of each discovery zone, respectively. The information regardingthe partitioning of these D2D discovery regions may be semi-staticallysignaled by the eNB using RRC signaling or by System Information Blocks(SIBs) for within network coverage scenarios. For the partial networkcoverage scenario, such information may be forwarded by the coordinatorUE to the UEs that are outside network coverage. For out of networkcoverage scenario, the discovery zone may be predefined or broadcastedby the centralized D2D device.

In some embodiments, the N_(RB) ^(D2D) and n_(RB) ^(start) parametersare not included in the D2D zone configuration message, and instead, thefull system bandwidth, except the PUCCH region (at band edges), may bedesigned to be exclusively reserved for D2D discovery from systemperspective, although the scope of the embodiments is not limited inthis respect. In some embodiments, the parameter n_(SF) ^(start) may beconfigured as a periodicity for D2D discovery zone allocation.

Even for the case of UE-based open discovery, it would be beneficial toexploit potential network assistance in UE-specific discovery resourceallocation for transmission of discovery signals for the UEs inRRC_CONNECTED mode, and thereby improve the efficiency of the discoveryprocess. In this regard, each D2D Discovery Region (D2D-DZ) may befurther divided into two orthogonal time-frequency zones: (1)Non-contention-based D2D DZ (NCB-D2D DZ) for which the eNB allocatesperiodic resources for transmission of discovery signals and this regionis accessible to D2D UEs in RRC_CONNECTED mode; (2) Contention-based D2DDZ (CB-D2D DZ): This region is, in general, available to all D2D UEs(including out of coverage UEs) wherein D2D-enabled UEs follow a purelycontention-based transmission of discovery signals. Moreover, the D2Ddiscovery resources used for CB-D2D DZ might be further divided into twoparts, called Part A and Part B to enable D2D discovery and to roughlyindicate the required size of D2D communication resources (e.g., thenumber of subframes for D2D communication) depending of the amount ofD2D data buffered at UE side, especially due to the fact that D2Ddiscovery procedure may be followed by a D2D communication operation.The use of a D2D discovery resource from one group indicates preferencefor the larger amount of resources then one predefined threshold.

In accordance with some embodiments, a D2D discovery zone may beconfigured in two distinct ways: network-common D2D discovery zone andcell-specific D2D discovery zone, the details of which are describedbelow. For network-common discovery zones, a common set oftime-frequency resources may be reserved for D2D discovery across theentire network. The configuration could be different between differentPublic Land Mobile Networks (PLMNs) to enable the respective operators acertain degree of flexibility in resource provisioning. The discoveryzone may be provisioned by each PLMN via the Operations, Administration,and Maintenance (OAM) tools. Network-common configuration of discoveryzones may be signaled via multiple ways. The exact resource provisioningmay be determined based on the statistics of the number of ProSe-enabledUEs in the network, their respective capabilities and location (up tothe tracking area (TA) granularity). This information is available atthe D2D server and the D2D server can inform the eNBs of the exactresource configuration via the Mobility Management Entity (MME).

For cell-specific discovery zones, each eNB 104 may determine the exactresource configuration for the cell-specific discovery zones usinginformation on the current number of active ProSe-enabled UEs 102 andthe interference situation. Some of this information may be obtained viaperiodic/event-triggered/on-demand feedback from the ProSe-enabled UEs102 participating in the discovery process. To enable inter-eNB D2Ddiscovery, a certain level of coordination between neighboring eNBsexists and may be achieved via exchange of information on theconfiguration of discovery zones between neighboring eNBs over an X2interface.

In accordance with embodiments, an eNB 104 may transmit signaling toindicate D2D discovery zone configuration to ProSe-enabled UEs 102. Thesignaling may indicate time and frequency resources and a periodicity ofthe discovery zone 204 and may indicate operational parameters for thediscovery zone 204. The resources of the D2D discovery zone 204 may beallocated for D2D discovery signal transmission by the ProSe-enabled UEs102.

In some embodiments, the D2D discovery zone configuration signaling mayindicate one or more occurrences of the discovery zone 204 and is sentby the eNB 104 either semi-statically using radio-resource control (RRC)signaling or sent using SIBs. In the example illustrated in FIG. 2, thediscovery zone 204 comprises a plurality of PRBs 206 within an LTEoperation zone 202 and the discovery zone 204 may occur periodically orregularly.

In some embodiments, the signaling is sent by the eNB either usingdedicated RRC signaling or sent using common radio-resource control(RRC) signaling via SIBs (i.e., SIB signaling). When the signaling sentby the eNB uses common RRC signaling via SIBs, the signaling sent by theeNB may include at least one of a SIB transmission and a pagingtransmission. In some embodiments, the configuration information mayeither added to an existing SIB (e.g., in accordance with LTE Release11) or is signaled via a newly defined SIB (e.g., in accordance with allater LTE release).

For signaling in the case of both network-common and cell-specificdiscovery zone allocation, the network should be able to signal thisinformation to UEs in both RRC_CONNECTED and RRC_IDLE modes ofoperation. For network-common D2D discovery zone allocation, differentsignaling mechanisms may be applied. In some embodiments, existingsystem information block (SIBs) (e.g., SIB2) may be used to signal theD2D discovery zone configuration information including silencing factorand other related cell- or network-common parameters discussed in moredetail below.

In some embodiments, the discovery zone 204 may be referred to orconsidered a discovery period. In some embodiments, contention-based D2Ddiscovery may be referred or considered Type 1 discovery whilenon-contention based D2D discovery may be referred to or considered Type2 discovery.

In some embodiments, the D2D discovery zone configuration signalingindicates at least one of a non-contention-based D2D discovery zone(NCB-D2D DZ) for which periodic resources are allocated fornon-contention based transmission of discovery signals 101 by onlyProSe-enabled UEs in RRC connected mode, and a contention-based D2Ddiscovery zone (CB-D2D DZ) for which periodic resources are allocatedfor contention-based transmission of discovery signals 101 by anyProSe-enabled UEs including ProSe-enabled UEs in RRC connected mode, RRCidle mode and out of coverage UEs. In these embodiments, thenon-contention-based D2D discovery zone may be designated fortransmission of discovery signals 101 in accordance with anon-contention based technique by ProSe-enabled UEs in RRC connectedmode. In some embodiments, ProSe-enabled UEs in RRC connected mode maybe assigned specific discovery resources of the non-contention-based D2Ddiscovery zone for their transmission of discover signals 101. In someembodiments, the D2D discovery zone configuration signaling may indicatethat the discovery zone 204 is partitioned into a non-contention-basedD2D discovery zone and a contention-based D2D discovery zone.

In some of these embodiments, the contention-based D2D discovery zonemay be designated for transmission of discovery signals 101 inaccordance with a purely contention based technique by any ProSe-enabledUE. In these embodiments, ProSe-enabled UEs are not assigned specificdiscovery resources of the contention-based transmission of discoversignals 101. ProSe-enabled UEs that utilize the contention-based D2Ddiscovery zone may include ProSe-enabled UEs in RRC connected mode,ProSe-enabled UEs in RRC idle mode, and other ProSe-enabled UEs such asout of coverage UEs (e.g., UEs connected to other eNBs).

In some of these embodiments, an eNB 104 may provide the signaling ofD2D discovery resources and both contention-based and contention-freeD2D discovery resources may be partitioned and configured by the eNB. Insome embodiments, the partitioning may be logical. For the actualpartitioning of resources, it would eventually be up to the network orthe eNB, (i.e., based on implementation). In some embodiments, some ofthe physical resources overlap between the two zones/resource pools,although the scope of the embodiments is not limited in this respect.

In some embodiments, application layer signaling may be used to signalthe D2D discovery zone configuration. In these embodiments, a D2D servermay signal the D2D discovery zone configuration during D2D registrationof the ProSe-enabled UEs. Changes to the D2D discovery zoneconfiguration may be signaled to the ProSe-enabled UEs by applicationlayer reconfiguration messages from the D2D server.

In some embodiments, non-access stratum (NAS) signaling may be used tosignal the D2D discovery zone configuration. In these embodiments, amobility management entity (MME) may signal the D2D discovery zoneconfiguration during D2D registration of the ProSe-enabled UEs with aD2D server. In these embodiments, either the UE or the D2D server mayrequest the discovery zone information. For both of the above signalingoptions (application layer or NAS signaling), it may be less efficientto support contention-free resource allocation to RRC_CONNECTED UEsbecause discovery zone resource is managed by the MME instead of the eNBand consequently, dynamic resource allocation is not preferred due tothe signaling overhead in core network.

FIG. 3A illustrates the reporting of discovery zone metrics inaccordance with some embodiments. In these embodiments, an eNB 104(FIG. 1) may be configured to receive discovery zone loading metrics,the discovery zone loading metrics based on monitoring of discoverysignals 101 (FIG. 1) within the discovery zone 204 (FIG. 2) by one ormore ProSe-enabled UEs 102 (FIG. 1). The eNB 104 may determine whetheror not to make changes to a resource allocation configuration for D2Dactivities based on the discovery zone loading metrics. In theseembodiments, ProSe-enabled UEs 102 may monitor the discovery zone 204for D2D discovery signals 101 transmitted by other ProSe-enabled UEs 102and report discovery zone loading metrics to the eNB 104. Based on thediscovery zone loading metrics, the eNB 104 may make changes to itsresource allocation configuration for D2D activities including resourcesfor D2D discovery and resources for D2D communications. In someembodiments, based on the discovery zone loading metrics, the eNB 104may make changes to optimize the resource allocation configuration forD2D activities. For example, the eNB 104 may change the size of theresource pool for D2D activities and may allocate subsequent discoverzone resources as well as allocate resources for subsequent D2Dcommunication based on the discovery zone loading metrics. Based on thediscovery zone loading metrics, the eNB 104 may also apply or suspendone or more interference control techniques, for example, by changingparameters for interference suppression (such as random silencing orrandom probabilistic transmission). As illustrated in FIG. 3A, aProSe-enabled UE 102 may receive signaling 312 indicating a discoveryzone configuration from an eNB 104. The UE 102 may monitor the discoveryzone in operation 313 and may report discovery zone metrics in message314.

In some embodiments, the discovery zone metrics include a count ofdiscovery signal transmissions in a number of occurrences of thediscovery zone (e.g., a count number). In some embodiments, thediscovery zone metrics further include a number of unique discoverysignal transmissions, and the eNB may determine a number ofProSe-enabled UEs 102 based on the discovery zone loading metrics. Insome embodiments, the discovery zone metrics may include at least oneof: a number of discovery signal transmissions in a number ofoccurrences of the discovery zone; a number of successfully detecteddiscovery signals in a number of occurrences of the discovery zone; andan indication of the interference level in a number of occurrences ofthe discovery zone. In some of these embodiments, ProSe-enabled UEs maybe able to distinguish the discovery signal transmissions of other UEsbased on the DMRS, and the discovery zone metrics may include a numberof blindly detected unique DMRS sequences or unique cyclic shift values.

In these embodiments, UEs may be configured to provide feedback forconfiguration of D2D discovery zones. For the case of cell-specificdiscovery zone configurations, the eNB may receive information on theloading in the cell from ProSe-enabled UEs participating in thediscovery process. However, an eNB may only know about the number ofsuch ProSe-enabled UEs in RRC_CONNECTED mode. The eNB may not be awareof the number of the RRC_IDLE mode UEs participating in D2D discoverywithin its serving area. Some embodiments provide the eNB with theinformation about the loading of the discovery zones are realized viaenabling UE feedback.

In some embodiments, ProSe-enabled UEs may report the number oftransmissions in the past N discovery zones, where N may be apre-determined or configurable parameter, in the form of a pagingresponse. Since the paging cycle may be configured in a UE-specific waywith different groups of UEs assigned different subframes for monitoringpaging, the number of UEs initiating a random access (RA) procedure as apaging response to provide this feedback may be managed by the eNB. Notethat given the low duty cycle of the configuration of the discoveryzones, it would not be necessary for the eNB to request for thisfeedback from all RRC_IDLE mode UEs at the same paging subframe toestimate the amount of loading of the discovery zones. Since thesilencing factor may be configured by the eNB, its impact may befactored in by the eNB in deriving this estimate.

The request for the feedback on number of transmissions in the past Ndiscovery zones may be added to the paging message and enabled by theeNB when it requires a UE or a set of UEs to report this metric.Additionally, the number of RRC_CONNECTED mode UEs participating in D2Ddiscovery may be known to the eNB by using the above mechanism or viafeedback requests indicated via dedicated RRC or MAC CE signaling.

In some other embodiments, a UE may report discovery related metrics ormeasurement reporting similar to Minimization Driving Test (MDT) or as apart of MDT reporting. In idle mode, the UE stores and accumulates themeasurement and reports the logged measurement once the UE is connected.In connected mode, the UE can report discovery related measurement in aperiodic or event-triggered manner. Since reporting is not immediate incase of idle mode, time stamp that indicates the moment of loggingmeasurement results may need to be included. In addition, the detailedlocation related information (e.g. cell index or GPS information) may bealso included. For discovery related metrics or measurements, asdescribed above, the number of transmissions in the past N discoveryzones may be reported. Alternatively, the interference level or thenumber of successfully detected D2D discovery packet transmissions maybe reported. For instance, assuming discovery packet transmissions usingrandomly selected DM-RS base sequences and/or cyclic shifts (forPUSCH-based discovery packet transmission), the UEs can report thenumber of blindly detected unique DM-RS sequences or cyclic shiftssummed or averaged over the most recent N1 D2D discovery zone, where N1may be pre-determined or configurable.

FIG. 3B illustrates the use of a random-access channel (RACH) to countProSe-enabled UEs in accordance with some embodiments. In theseembodiments, the eNB 104 may determine the number of ProSe-enabled UEs102 based on radio-resource control (RRC) signaling (operation 308)received from the ProSe-enabled UEs 102 during a contention-based randomaccess (CBRA) procedure 300 as part of an initial access procedure. TheRRC signaling may, for example, include a D2D capability indication ofthe transmitting ProSe-enabled UE 102. In these embodiments, the eNB 104may determine whether or not to make changes to a resource allocationconfiguration for D2D activities based on the discovery zone loadingmetrics and the number of ProSe-enabled UEs 102 determined based on theRRC signaling.

In these embodiments, the RACH is used for D2D UEs counting: Counting ofProSe-enabled (i.e., D2D capable) UEs is performed during UE's initialContention-Based Random Access (CBRA) procedure (operations 302, 304,306, 308 and 310). In these embodiments, a UE's ProSe-capability may beincluded in the message transmitted operation 308. These embodiments maybe used to count RRC_CONNECTED as well as RRC_IDLE mode UEs.

FIG. 4 illustrates a procedure for counting ProSe-enabled UEs for UEs inradio-resource control (RRC) connected mode. In these embodiments, aneNB 104 may be configured to transmit a D2D counting request message(operation 402) and receive a D2D counting response message (operation404) from ProSe-enabled UEs 102 that are in radio-resource control (RRC)connected mode. In these embodiments, the D2D counting response message404 may indicate that the responding UE is a ProSe-enabled UE allowingthe eNB 104 to coarsely estimate the number of ProSe-enabled UEs basedon the number of D2D counting response messages 404 that are received.In some of these embodiments, a D2D counting response message 404 may beindicate that a UE in RRC connected mode is not ProSe-enabled.

In some embodiments, the D2D counting request message (operation 402)may include plurality of dedicated RACH preambles allocated for D2Dcounting and the D2D counting response message (operation 404) maycomprise one of the RACH preambles selected by a ProSe-enabled UE 102and transmitted within an assigned access slot (e.g., a RACHtime/frequency resource).

In these embodiments, a set of dedicated RACH preambles may be includedin D2D counting request message. Upon receiving a counting request fromthe network for D2D counting purpose, a D2D-capable UE responds bysending a RACH preamble selected from the pool of RACH preamblesallocated for D2D UE counting purpose; the UE transmits the selectedpreamble on the assigned access slot (RACH channel time/frequencyresource). Note that, a relatively coarse estimation of the number ofD2D-capable UEs may be sufficient to determine whether D2D discoveryresources need to added or reduced compared to the current configuration(that may be achieved by comparing to a certain threshold number thatrelates to the current D2D resource configuration). A very accuratecounting of larger numbers of UEs is not necessary. Therefore byallocating a number of preamble signature-timeslot combinations similarto or only a little greater than this threshold number, it isstraightforward to derive the required information.

In these embodiments, counting the D2D capable UEs in RRC_CONNECTED modemight be sufficient in some cases for optimized discovery resourcesallocation due to the fact that discovery signal resources is typicallyallocated in a semi-static manner and any RRC_IDLE Mode D2D capable UEhas to use the contention-based resources for D2D discovery due to lackof RRC context in the radio-access network. The network has thecapability to gradually adjust the resources according to the detectedstatistics of the D2D resource utilization and the likelihood ofcollisions. Therefore, as defined as part of the MBMS countingprocedure, the E-UTRAN first initiates the procedure by sending aD2DCountingRequest message. Upon receiving the D2DCountingRequestmessage, the UE capable of D2D discovery in RRC_CONNECTED mode shalltransmit a D2DCountingResponse message.

In some embodiments, an eNB may determine the number of ProSe-enabledUEs 102 based on RRC messages indicating discovery resource releasetransmitted by ProSe-enabled UEs in RRC connected mode. In some of theseembodiments, ProSe-enabled UEs in RRC_CONNECTED mode can transmit an RRCmessage indicating discovery resource release even if they have not yetbeen configured with dedicated discovery resources. This information canassist the eNB in estimating the number of ProSe-enabled UEs inRRC_CONNECTED mode participating in D2D discovery, and can therebyoptimize the resource allocation for RRC_CONNECTED mode UEs.

In some embodiments the eNB may determine the number of ProSe-enabledUEs 102 based on reception of periodic tracking area (TA) messageshaving a D2D capability indication transmitted by ProSe-enabled UEs inRRC idle mode. In these embodiments, ProSe-enabled UEs in RRC idle modemay be configured to add the D2D capability indication to the periodictracking area (TA) messages.

In some embodiments, a ProSe-enabled UE may be configured to receivedevice-to-device (D2D) discovery zone configuration signaling from anenhanced node B (eNB) to indicate time and frequency resources and aperiodicity of a discovery zone and to indicate one or more discoveryzone operational parameters. In some embodiments, when a UE is inradio-resource control (RRC) idle mode (RRC_IDLE), the UE may transitionto RRC connected mode (RRC_CONNECTED) to send a discovery resourcerequest to the eNB. The UE may autonomously switch back to the RRC idlemode upon reception of a resource configuration message from the eNB, atleast for transmission in a contention-based D2D discovery zone (CB-D2DDZ).

In some embodiments, an eNB 104 may be configured to exchange D2Ddiscovery zone configuration information with one or more neighbor eNBs.The eNB 104 may be configured to signal the D2D discovery zoneconfiguration information of the one or more neighbor eNBs toProSe-enabled UEs (e.g., via SIB signaling). In these embodiments, acertain level of coordination between the neighboring eNBs may supportof inter-eNB discovery, especially for the case of cell-specificconfiguration of D2D discovery zones. In some embodiments, eNBs 104 mayexchange information on the configuration of D2D discovery zones intheir respective cells. The D2D discovery configuration of a neighboringcell may be signaled to the UEs 102 by the respective serving cells. Insome alternate embodiments, the serving cell may inform the UEs aboutthe location of the relevant system information block (SIB) transmittedby the neighboring cells and the UEs may acquire the corresponding SIBand thereby know the D2D discovery zone configuration in neighboringcells. For both cases, it may be up to UE implementation, especially forUE-based open discovery, as to whether to transmit and/or listen on theD2D discovery zones (that do not overlap with its serving cell D2Ddiscovery zone) of all the cells in its neighbor cell list of only aselected subset thereof.

For network-common configuration of D2D discovery zones, constituentcells may be configured to maintain tight time-synchronization withrespect to subframe boundary, subframe number (SFN), etc. to enable acommon D2D discovery zone. This may be achieved, for instance, usingbackhaul-based synchronization or using GPS. In some embodiments, therequirements on tight time-synchronization may be relaxed by using anextended cyclic prefix (CP) for the D2D discovery zones and using anormal-length cyclic prefix for non-discovery zones.

For D2D discovery zones that are configured on a cell-specific basis,one challenge arises from the issue of coexistence of D2D discoverytransmission/reception and cellular (WAN) traffic. Since the D2Ddiscovery zones are configured in the currently defined UL subframes,the inter-cell interference between D2D discovery signal transmissionsand UL PUSCH transmissions may be managed, for example, by UL schedulingand UL power control for PUSCH transmissions, incorporating some form oftransmit power control (e.g., by configuring the maximum transmit power)for transmission of discovery signals, employing a cell-clusteringapproach, and/or the selection of discovery resources by the UE based onUE geometry. These embodiments are discussed in more detail below.

In some embodiments, to signal the D2D discovery zone configurationinformation of the one or more neighbor eNBs, the eNB 104, whenoperating as a serving eNB is configured to provide location informationfor system information blocks (SIB) transmitted by one or moreneighboring eNBs to allow UEs being served by the serving eNB to acquirethe SIBs, the SIBs indicating D2D discovery zone configuration for theone or more neighboring eNBs. In these embodiments, it may be up to theUE implementation, especially for UE-based open discovery, as to whetherto transmit and/or listen on the D2D discovery zones (that do notoverlap with its serving cell D2D discovery zone) of all the cells inits neighbor cell list of only a selected subset thereof. In theseembodiments, the UE may receive the signaling from a serving eNB when inRRC connected mode and may receive the signaling from an eNB that the UEis camping on when the UE is in RRC idle mode. In accordance withembodiments, a UE has a serving eNB when in RRC connected mode, whilewhen in RRC idle mode, the UE camps on an eNB (since it is not beingservice by an eNB when in idle).

In some embodiments, an eNB 104 is configured to exchange D2D discoveryzone configuration information one or more neighbor eNBs. Based the D2Ddiscovery zone configuration information of the one or more neighboreNBs, the eNB 104 may be configured to engage in an inter-cellinterference reduction technique to reduce intra-cell and inter-cellinterference within the discovery zone and inter-cell interferencebetween discovery signal transmissions and uplink cellulartransmissions. The inter-cell interference reduction technique includeone or more of:

-   -   performance of cooperative subframe power control for D2D        discovery signal transmissions wherein uplink subframe sets are        configured with separate power control parameters for        interference reduction between the uplink cellular transmissions        (e.g., physical uplink shared channel (PUSCH) transmissions) and        the D2D discovery signal transmissions;    -   configuration of transmit power control levels for transmission        of discovery signals;    -   employment of cooperative cell clustering to align discovery        zones of the one or more neighbor eNBs; and    -   employment of geometry-based intra-cell discovery zone        partitioning.

FIG. 5 illustrates cooperative uplink subframe power control for D2Ddiscovery signal transmission in accordance with some embodiments. Insome of these embodiments, UL scheduling and UL power control for PUSCHtransmissions may be configured by the serving cell as the configurationof the D2D discovery zone in the neighboring cells is known by theserving cell. In some embodiments, two UL subframe sets may beconfigured to have separate power control parameters (e.g. open-looppower control parameters PO and alpha) for different UL subframe sets.This may avoid strong inter-cell interference from cellular PUSCHtransmission to D2D discovery signal reception of neighboring cell byusing one UL subframe set to cover the D2D discovery resources ofneighboring cell(s) as illustrated in FIG. 5.

Some embodiments may incorporate a form of transmit power control (e.g.,by configuring the maximum transmit power) for transmission of discoverysignals. In some embodiments, multiple maximum power classes for D2Ddiscovery signal can predefined and the selected maximum transmit powerlevel may be signaled to UE through D2D discovery configurationsignaling.

Some embodiments may employ a cell-clustering approach wherebyneighboring cells align their D2D discovery zone configurations viainformation exchange via X2 115 (FIG. 1). In these embodiments, only thetime-frequency resources reserved for D2D discovery zones may need to bealigned and each cell can configure a silencing factor (discussed inmore detail below) independently to adjust for variations in the loadingof the D2D discovery zones to manage intra-cell/intra-clusterinterference within the D2D discovery zones.

In some embodiments, the discovery zone operational parameters mayinclude at least one of a silencing factor, a transmit power controlconfiguration, hopping related parameters and a scrambling ID. In theseembodiments, irrespective of the type of D2D discovery operation: openor restricted discovery, for RRC_CONNECTED or RRC_IDLE ProSe-enabledUEs, certain parameters related to configuration and transmission ofdiscovery zones and signals (e.g., discovery packets) may be signaled tothe corresponding UEs.

In these embodiments, the discovery zone configuration may include anypartitioning of the overall zone into contention-based andcontention-free discovery zones. Parameters may be included to indicatethe extent of each discovery zone in the time and frequency domains, andmay indicate a time offset and a periodicity of the configuration of thezones. For a cell-specific discovery zone allocation, this informationwould be cell specific and a serving cell may signal the parameterscorresponding to the neighboring cells to support inter-eNB discovery.

In some embodiments, if fixed random silencing is configured, a singlevalue for the silencing factor may be signaled. On the other hand, forsupport of more advanced adaptive silencing mechanisms, more than oneparameter may need to be signaled. In one embodiment, each ProSe-enabledUE 102 may be configured with a nominal silencing factor that is appliedfor the first occurrence of the discovery zone for the respective UE.For the subsequent discovery zone occurrences, the silencing factor tobe applied by the UE may be incremented or decremented within certainlower and upper bounds (by certain factors signaled by the network/eNB)depending on whether the UE transmitted in the previous zone or not. Thebounds may either be static (preconfigured) or configured and updated bythe network and/or the eNB at a very slow rate, although the scope ofthe embodiments is not limited in this respect.

In some embodiments, the eNB may be configured to reduce interferencewithin the discovery zone by employing a silencing and muting protocolfor discovery signal transmissions and configured to include thesilencing factor in the discovery zone parameters. In these embodiments,the silencing and muting protocol configures the ProSe-enabled UEs withthe silencing factor for use in D2D discovery signal transmission onrandomly selected resources of the D2D discovery zone based onprobability indicated by the silencing factor. The effective arrivalrate of the discovery packets and thereby the interference level withinthe D2D discovery zones may be controlled. In these embodiments, eachProSe-enabled UE that intends to transmit a discovery packet mayrandomly selects a resource from within the D2D discovery zone and maytransmit the packet with a certain probability (e.g., (1-p), with0≦p≦1). In these embodiments, p may be defined as the silencing factoror transmission probability factor that is configured by the network,either in a network-common manner or in a cell-specific manner byindividual serving cells.

In some embodiments, the signaling to the UE indicates that thesilencing factor is to be either incremented or decremented for use insubsequent occurrences of the discovery zone depending on whether the UEtransmitted D2D discovery zones in a prior occurrence of the discoveryzone.

In some embodiments, when the discovery zone parameters comprise includethe transmit power control configuration, a UE may be configured with amaximum transmit power for transmission of D2D discovery signals that islower than a transmit power specified by a respective UE category. Inthese embodiments, depending on the discovery traffic conditions and usecases, ProSe-enabled UEs may be configured with a maximum transmit powerthat may be lower than that specified by the respective UE category. Themaximum transmit power may be applied for discovery packet transmission.If supported, additional parameters related to more advanced adaptivepower control options would need to be signaled as well.

In some embodiments, when the discovery zone parameters comprise includethe hopping related parameters, the hopping related parameters indicate:

-   -   parameters for discovery resource hopping in a contention-free        D2D discovery zone configuration;    -   a hopping type comprising either type 1 or type 2 hopping;    -   a hopping mode comprising either intra-subframe or        inter-subframe hopping;    -   a subband size for the type 2 hopping; and    -   a pseudorandom sequence initialization for the type 2 hopping.

In these embodiments, for contention-free discovery resourceallocations, certain randomized hopping related signaling may beprovided to the UE. Further, for payload-based transmissions wherein theeach discovery packet transmission spans multiple PRB-pairs, differenttypes of intra- or inter-subframe hopping may be configured.

In some embodiments, when the discovery zone parameters comprise includethe scrambling identity, the scrambling identity may to be used forscrambling of a CRC mask of the D2D discovery packets. A commonscrambling ID may be assigned per discovery group. In these embodiments,a scrambling Identity (ID) may be used for scrambling of the CRC mask ofthe discovery packets. The scrambling identity may be common perdiscovery group. For open discovery, all ProSe-enabled UEs within thenetwork (for network-common discovery resource configuration) or withincells or cell-clusters (for cell-specific discovery resourceconfiguration) may be configured with a common scrambling ID.

For restricted discovery, the scrambling ID may be used for filtering ofdecoded candidates by the discovering UE before sending the list ofcandidates to the upper layers for verification for restricteddiscovery. For closed discovery, the scrambling is the same on aper-white list basis for restricted discovery. In this way, thoseProSe-enabled UEs that are not on white list will not be able to decodethe packet. The closed group scrambling seed should be generated by theD2D server, and sent together with the white list group informationduring D2D registration (not through SIB/paging).

In some embodiments, for restricted discovery, a temporary identifier(Temp_ID) may be used to differentiate the same ProSe-enabled UEbelonging to different discovery groups (different white lists of otherProSe-enabled UEs). Each ProSe-enabled UE transmitting as part ofrestricted discovery is assigned with one or more Temp_IDs that replacethe UE identity in the discovery packet. When a discovering UE decodessuch a packet, it forwards the decoded Temp_ID(s) to the network forfurther identification and verification as part of the restricteddiscovery process. For example, consider three ProSe-enabled UEsparticipating in restricted discovery: UE_A, UE_B, and UE_C. UE_A andUE_B belong to distinct groups A and B respectively and don not haveeach other in their respective white lists, while UE_C is in both thewhite lists. Then, UE_C may be assigned two distinct Temp_IDs (UE_Ca andUE_Cb) such that both UE_A and UE_B can discover UE_Ca and UE_Cbrespectively, and thereby, with subsequent identification from thenetwork, can discover UE_C. However, UE_A and UE_B can only discovereach other via open discovery operation.

FIG. 6 illustrated eNB-triggered contention-free D2D discovery zoneresources in accordance with some embodiments. In these embodiments, aneNB may use RRC and/or Layer 1 (physical layer) signaling to indicate asemi-persistent allocation of discovery resources to a ProSe-enabled UEin RRC connected mode for contention-free transmission of D2D discoverysignals. The eNB may be configured to release the allocation ofdiscovery resources by transmission of a discovery resource release. Inthese embodiments, contention-free mode of D2D discovery may besupported in multiple ways. In some embodiments, this mode of operationmay be triggered by the eNB (operation 602) in which the eNB configuresone or more RRC_CONNECTED mode ProSe-enabled UEs with dedicatedresources for transmission of discovery signals in operation 604. Theresource allocation in this case may be realized in the form ofsemi-persistent allocation of discovery resources using a combination ofRRC and Layer 1 signaling (operation 606). The configured dedicatedresources may also be released (operation 608) by the eNB depending onthe loading and overall D2D discovery resource allocation state.

FIG. 7 illustrated UE-triggered contention-free D2D discovery zoneresources in accordance with some embodiments. In these embodiments, aneNB may allocate discovery resources to a ProSe-enabled UE in RRCconnected mode for contention-free transmission of D2D discovery signalsin response to a RRC resource request from the ProSe-enabled UE. Inaddition to eNB-decided discovery resource release, the eNB may releasethe allocation of discovery resources in response to reception of aresource release request via RRC signaling from the ProSe-enabled UEs.In these embodiments, an RRC_CONNNECTED UE, for example, on initiationfrom higher layers, may request (operation 702) the serving cell forresources for D2D discovery signal transmissions via RRC layer.Subsequently, subject to eNB decision, the serving cell may configurethe UE via RRC signaling with the configuration of the resourceallocation (operation 704) and eventually semi-persistent allocationsvia Layer 1 signaling. The layer 1 signaling/activation is no used sinceresources may be configured via RRC (operation 704) and then thediscovery transmission automatically gets activated starting from thenext occurrence of the discovery resource pool/zone (operation 706). Inaddition to eNB-decided release of the resources (operation 710), a UEcan also request for discovery resource release via RRC layer (operation708).

In these embodiments, when the D2D discovery resources are explicitlyallocated via PDCCH, the RRC resource configuration (operation 704) maynot be required. Combinations of eNB-triggered, UE-triggeredcontention-free resource allocation schemes with eNB-decided andUE-requested resource release mechanisms may be realized as well.

Additionally, resources for D2D discovery may not be reserved (i.e., nodiscovery zones configured) at a cell-/cell-cluster-level ornetwork-level depending on presence of active ProSe-enabled UEs. In sucha situation, a ProSe-enabled UE in RRC_CONNECTED mode can send a requestfor allocation of D2D discovery resources via RRC or application layer.If it is requested via application layer, this request will be sent toD2D server which, in turn, requests the eNB to turn on discovery zone orallocate additional resources for contention-free discovery as required.Also, a ProSe-enabled UE in RRC_IDLE mode can transit to connected modeto send discovery resource request. However, it may not involve RRCconnection set up. For example, the UE can send RRC connect request onlyindicating discovery zone request. Alternatively, the UE autonomouslygoes to idle mode when the eNB sends acknowledgement (or discovery radioresource configuration) message for the discovery request message.

In some embodiments, D2D discovery resources may be staticallyprovisioned. For support of D2D discovery for national security andpublic safety (NSPS) use cases in outside or partial network coveragescenarios, certain periodic time-frequency resources may bepre-configured for the public safety (PS) ProSe-enabled UEs as D2Ddiscovery resources. Such resources could be configured to have a lowduty cycle and under appropriate conditions, depending on the exact D2Ddiscovery protocol, additional resources may be allocated to supplementthe preconfigured D2D discovery zones by coordinating UEs for partial oroutside network coverage scenarios. The configuration of the additionalresources can follow the principles outlined above with consideration ofthe presence of the statically preconfigured default D2D discoveryzones.

In some embodiments, for geometry-based intra-cell D2D discovery zonepartitioning, a UE may receive signaling from a serving eNB indicatingD2D discovery zone configuration information of one or more neighboreNBs including discovery resources of the D2D discovery zone used for atleast one of cell-center D2D UEs and cell edge D2D UEs. The UE mayselect resources indicated for cell-center D2D UEs or cell edge D2D UEsfor transmission of D2D discovery signals based at least on an RSRP of aserving eNB. In these embodiments, a UE may select a discovery resourcebased on UE geometry. The discovery zone may be divided and some ofdiscovery resource is mainly used for cell-center UEs if these discoveryresources are used for normal UL scheduling in neighboring cells. TheProSe-enabled UEs that have the ratio RSRP_(serving)/RSRP_(strongest)_(—) _(neighbor) greater than some pre-defined or configured thresholdcan transmit D2D discovery packets in the discovery zone reserved forcell-center ProSe-enabled UEs. In the above, RSRP_(serving) is theserving cell RSRP and RSRP_(strongest) _(—) _(neighbor) corresponds tothe RSRP for the link to the cell in the neighbor cell list with themaximum RSRP value. This geometry-based intra-cell D2D discovery zonepartitioning coupled with careful scheduling of PUSCH transmissions inthe cells with WAN traffic can enable co-existence of D2D discoveryzones and LTE UL transmissions in neighboring cells. The eNBs canexchange information on the discovery resource used for cell center D2DUEs or cell edge D2D UEs. In some of these embodiments, the UE mayselected the discovery resource based on RSRP_(serving) instead of theratio and would work similarly, especially in NWs with eNBs with similartransmission power (e.g., for macro-only networks.

FIG. 8 illustrates a functional block diagram of a wirelesscommunication device in accordance with some embodiments. Wirelesscommunication device (WCD) 800 may be suitable for use as a UE 102(FIG. 1) or an eNB 104 FIG. 1). The WDC 800 may include physical layer(PHY) circuitry 802 for transmitting and receiving signals to and fromother WDCs (eNBs and UEs) using one or more antennas 801 as well as forD2D communications with other UEs. WDC 800 may also include mediumaccess control layer (MAC) circuitry 804 for controlling access to thewireless medium. WDC 800 may also include processing circuitry 806 andmemory 808 arranged to configure the various elements of the WDC 800 toperform the various operations described herein.

In some embodiments, the mobile device may be part of a portablewireless communication device, such as a personal digital assistant(PDA), a laptop or portable computer with wireless communicationcapability, a web tablet, a wireless telephone, a smartphone, a wirelessheadset, a pager, an instant messaging device, a digital camera, anaccess point, a television, a medical device (e.g., a heart ratemonitor, a blood pressure monitor, etc.), or other device that mayreceive and/or transmit information wirelessly. In some embodiments, themobile device may include one or more of a keyboard, a display, anon-volatile memory port, multiple antennas, a graphics processor, anapplication processor, speakers, and other mobile device elements. Thedisplay may be an LCD screen including a touch screen.

The antennas 801 may comprise one or more directional or omnidirectionalantennas, including, for example, dipole antennas, monopole antennas,patch antennas, loop antennas, microstrip antennas or other types ofantennas suitable for transmission of RF signals. In some multiple-inputmultiple-output (MIMO) embodiments, the antennas may be effectivelyseparated to take advantage of spatial diversity and the differentchannel characteristics that may result.

Although the mobile device is illustrated as having several separatefunctional elements, one or more of the functional elements may becombined and may be implemented by combinations of software-configuredelements, such as processing elements including digital signalprocessors (DSPs), and/or other hardware elements. For example, someelements may comprise one or more microprocessors, DSPs,field-programmable gate arrays (FPGAs), application specific integratedcircuits (ASICs), radio-frequency integrated circuits (RFICs) andcombinations of various hardware and logic circuitry for performing atleast the functions described herein. In some embodiments, thefunctional elements may refer to one or more processes operating on oneor more processing elements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage device, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage device may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagedevice may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. Some embodiments mayinclude one or more processors and may be configured with instructionsstored on a computer-readable storage device.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An enhanced node B (eNB) comprising hardwareprocessing circuitry configured to: transmit signaling to indicate adevice-to-device (D2D) discovery zone configuration to proximity service(ProSe) enabled user equipment (UE), the signaling to indicate time andfrequency resources and a periodicity of a discovery zone and toindicate operational parameters for the discovery zone, wherein theresources of the D2D discovery zone are allocated for D2D discoverysignal transmission by the ProSe-enabled UEs.
 2. The eNB of claim 1wherein the signaling for the D2D discovery zone configuration indicatesone or more occurrences of the discovery zone, and wherein the signalingis sent by the eNB either using dedicated radio-resource control (RRC)signaling or sent using common radio-resource control (RRC) signalingvia system information blocks (SIBs).
 3. The eNB of claim 1 wherein whenthe signaling sent by the eNB uses common RRC signaling via SIBs, thesignaling sent by the eNB includes at least one of a SIB transmissionand a paging transmission.
 4. The eNB of claim 2 wherein the signalingfor the D2D discovery zone configuration indicates at least one of: anon-contention-based D2D discovery zone (NCB-D2D DZ) for which periodicresources are allocated for non-contention based transmission ofdiscovery signals by only ProSe-enabled UEs in RRC connected mode; and acontention-based D2D discovery zone (CB-D2D DZ) for which periodicresources are allocated for contention-based transmission of discoverysignals by any ProSe-enabled UEs including ProSe-enabled UEs in RRCconnected mode, RRC idle mode and out of coverage UEs.
 5. The eNB ofclaim 2 further configured to: receive discovery zone loading metrics,the discovery zone loading metrics based on monitoring of discoverysignals within the discovery zone by one or more ProSe-enabled UEs; anddetermine whether or not to make changes to a resource allocationconfiguration for D2D activities based on the discovery zone loadingmetrics.
 6. The eNB of claim 2 wherein the eNB is configured to receiveD2D discovery zone configuration information of one or more neighboreNBs, and wherein the eNB is configured to signal the D2D discovery zoneconfiguration information of the one or more neighbor eNBs to the ProSeenabled UEs via SIB signaling.
 7. The eNB of claim 2 wherein the eNB isconfigured to receive D2D discovery zone configuration information ofone or more neighbor eNBs, and wherein based on the D2D discovery zoneconfiguration information of the one or more neighbor eNBs, the eNB isfurther configured to engage in an interference reduction technique toreduce intra-cell and inter-cell interference within the discovery zoneand inter-cell interference between discovery signal transmissions anduplink cellular transmissions, the technique to include one or more of:cooperative subframe power control for D2D discovery signaltransmissions wherein uplink subframe sets are configured with separatepower control parameters for interference reduction between the uplinkcellular transmissions and the D2D discovery signal transmissions;transmit power level control for the D2D discovery signal transmission;cooperative cell clustering to align discovery zones of the one or moreneighbor eNBs; and geometry-based intra-cell discovery zonepartitioning.
 8. The eNB of claim 7 wherein the discovery zoneoperational parameters include at least one of a silencing factor, atransmit power control configuration, hopping related parameters and ascrambling ID.
 9. The eNB of claim 8 wherein the eNB is furtherconfigured to reduce interference within the discovery zone by employinga silencing and muting protocol for discovery signal transmissions andconfigured to include the silencing factor in the discovery zoneparameters, and wherein the silencing and muting protocol configures theProSe-enabled UEs with the silencing factor for use in D2D discoverysignal transmission on randomly selected resources of the D2D discoveryzone based on probability indicated by the silencing factor.
 10. The eNBof claim 8 wherein when the discovery zone parameters comprise includethe transmit power control configuration, the ProSe-enabled UEs areconfigured with a maximum transmit power for D2D discovery signaltransmission that is lower than a transmit power specified by arespective UE category, wherein when the discovery zone parametersinclude the hopping related parameters, the hopping related parametersindicate: the parameters needed for discovery resource hopping in acontention-free D2D discovery zone; a hopping type comprising eithertype 1 or type 2 hopping; a hopping mode comprising eitherintra-subframe or inter-subframe hopping; a subband size for the type 2hopping; and a pseudorandom sequence initialization for the type 2hopping, and wherein when the discovery zone parameters include thescrambling identity, the ProSe enabled UEs are configured to use thescrambling identity for scrambling of a cyclic-redundancy check (CRC)mask of the D2D discovery packets, and the eNB is configured to assign acommon scrambling ID per discovery group.
 11. The eNB of claim 1 whereinthe signaling comprise one or more of radio-resource control (RRC) andLayer 1 signaling to indicate a semi-persistent allocation of discoveryresources to the ProSe enabled UEs in RRC connected mode forcontention-free transmission of D2D discovery signals, and wherein theeNB is configured to release the allocation of discovery resources bytransmission of a discovery resource release.
 13. The eNB of claim 12wherein the eNB allocates the discovery resources to the ProSe enabledUEs in RRC connected mode for contention-free transmission of D2Ddiscovery signals in response to a RRC resource request from the ProSeenabled UE; and wherein, the eNB is further configured to release theallocation of discovery resources in response to reception of a resourcerelease request via RRC signaling from the ProSe enabled UEs.
 14. Anenhanced node B (eNB) comprising hardware processing circuitry andconfigured to: transmit signaling to indicate a device-to-device (D2D)discovery zone configuration to proximity service (ProSe) enabled userequipment (UE), the signaling to indicate at least time and frequencyresources and a periodicity of a discovery zone; receive discovery zoneloading metrics, the discovery zone loading metrics based on monitoringof discovery signals within the discovery zone by one or moreProSe-enabled UEs; and determine whether or not to make changes to aresource allocation configuration for D2D activities based on thediscovery zone loading metrics.
 15. The eNB of claim 14 wherein thediscovery zone metrics include at least one of: a number of discoverysignal transmissions in a number of occurrences of the discovery zone; anumber of successfully detected discovery signals in a number ofoccurrences of the discovery zone; and an indication of the interferencelevel in a number of occurrences of the discovery zone, wherein the eNBis further configured to determine a number of the ProSe enabled UEsbased on the discovery zone loading metrics.
 16. The eNB of claim 14wherein the eNB is further configured to determine the number of theProSe enabled UEs based on radio-resource control (RRC) signalingreceived from the ProSe enabled UEs during a contention-based randomaccess (CBRA) procedure as part of an initial access procedure, whereinthe RRC signaling includes a D2D capability indication.
 17. The eNB ofclaim 14 further configured to: transmit a D2D counting request message;and receive a D2D counting response message from the ProSe enabled UEsthat are in radio-resource control (RRC) connected mode.
 18. The eNB ofclaim 14 wherein the eNB is further configured to determine the numberof the ProSe enabled UEs based on reception of periodic tracking area(TA) messages having a D2D capability indication transmitted by theProSe-enabled UEs that are in RRC idle mode.
 19. User Equipment (UE)enabled for proximity services (ProSe), the ProSe-enabled UE comprisinghardware processing circuitry and configured to: receivedevice-to-device (D2D) discovery zone configuration signaling from anenhanced node B (eNB) to indicate time and frequency resources and aperiodicity of a discovery zone and to indicate one or more discoveryzone operational parameters; and transmit D2D discovery signals withinthe resources to discover one or more other ProSe-enabled UEs.
 20. TheUE of claim 19 wherein when the UE is in radio-resource control (RRC)idle mode (RRC_IDLE), the UE is configured to transition to RRCconnected mode (RRC_CONNECTED) to send a discovery resource request to aserving eNB, and wherein the UE is further configured to autonomouslyswitch back to the RRC idle mode upon reception of a resourceconfiguration message from the serving eNB, at least for transmission ina contention-based D2D discovery zone (CB-D2D DZ).
 21. The UE of claim19 wherein the signaling for the D2D discovery zone configurationindicates one or more occurrences of the discovery zone and is sent bythe eNB either using dedicated radio-resource control (RRC) signaling orusing common radio-resource control (RRC) signaling via systeminformation blocks (SIBs), wherein the UE is further configured tomonitor the discovery zone for D2D discovery signals transmitted byother UEs; and report discovery zone loading metrics to the eNB based onthe monitored discovery signals, and wherein the discovery zone loadingmetrics comprise one or more of: a count of the number of D2D discoverysignals transmitted by other UEs during a number of occurrences of thediscovery zone; a count of the number of D2D discovery signalstransmitted by itself during a number of occurrences of the discoveryzone; and an indication of interference level in a number of occurrencesof the discovery zone.
 22. The UE of claim 21 wherein when the signalingfor the discovery zone configuration indicates a periodic occurrence ofthe discovery zone for which periodic discovery-zone resources areallocated for D2D discovery, the UE is further configured to: monitor anumber of the occurrences of the discovery zone for D2D discoverysignals transmitted by other UEs; and report the discovery zone loadingmetrics to the eNB based on the D2D discovery signals monitored in theoccurrences of the discovery zone.
 23. The UE of claim 19 wherein the UEis configured to receive signaling from the eNB indicating D2D discoveryzone configuration information of one or more neighbor eNBs, and whereinthe UE is further configured to: transmit D2D discovery signals in anindicated D2D discovery zone of the one or neighbor eNBs, and monitorthe indicated D2D discovery zone of the one or neighbor eNBs for D2Ddiscovery signals.
 24. The UE of claim 19 wherein the UE wherein forgeometry-based intra-cell D2D discovery zone partitioning the UE isconfigured to receive signaling from the eNB indicating D2D discoveryzone configuration information of a serving eNB and of one or moreneighbor eNBs including discovery resources of the D2D discovery zoneused for at least one of cell-center D2D UEs and cell edge D2D UEs, andwherein the UE is further configured to select resources indicated forcell-center D2D UEs or cell edge D2D UEs for transmission of D2Ddiscovery signals based at least on a reference signal received power(RSRP) of the serving eNB.
 25. The UE of claim 21 wherein the signalingfor the D2D discovery zone configuration is configured to indicate atleast one of: a non-contention-based D2D discovery zone (NCB-D2D DZ) forwhich periodic resources are allocated for non-contention basedtransmission of discovery signals by ProSe-enabled UEs in RRC connectedmode; and a contention-based D2D discovery zone (CB-D2D DZ) for whichperiodic resources are allocated for contention-based transmission ofdiscovery signals by the ProSe-enabled UEs including ProSe-enabled UEsin RRC connected mode, RRC idle mode and out of coverage ProSe-enabledUEs, wherein the UE is configured to monitor any signaled of the NCB-D2DDZs and CB-D2D DZs for discovery signals transmitted by other UEs. 26.The UE of claim 21 wherein the discovery signal transmissions include ademodulation reference signal (DMRS) sequence comprising a randomlyselected choice of at least one of a base sequence, a cyclic shift valueand an orthogonal cover code, and wherein the discovery zone metricsfurther include a number of blindly detected unique DMRS sequences. 27.A method performed by an enhanced node B (eNB) for signaling fordevice-to-device (D2D) discovery operations, the method comprising:transmitting signaling to indicate a D2D discovery zone configuration toproximity service (ProSe) enabled user equipment (UE), the signaling toindicate time and frequency resources and a periodicity of a discoveryzone and to indicate operational parameters for the discovery zone,wherein the resources of the D2D discovery zone are allocated for D2Ddiscovery signal transmission by the ProSe-enabled UEs, wherein thesignaling for the D2D discovery zone configuration indicates one or moreoccurrences of the discovery zone, and wherein the signaling is sent bythe eNB either using dedicated radio-resource control (RRC) signaling orsent using common radio-resource control (RRC) signaling via systeminformation blocks (SIBs).
 28. The method of claim 27 wherein when thesignaling sent by the eNB uses common RRC signaling via SIBs, thesignaling sent by the eNB includes at least one of a SIB transmissionand a paging transmission, and wherein the discovery zone operationalparameters include at least one of a silencing factor, a transmit powercontrol configuration, hopping related parameters and a scrambling ID.29. A non-transitory computer-readable storage medium that storesinstructions for execution by one or more processors to configure anenhanced node B (eNB) for signaling for device-to-device (D2D) discoveryoperations, the operations to configure the eNB to: transmit signalingto indicate a D2D discovery zone configuration to proximity service(ProSe) enabled user equipment (UE), the signaling to indicate time andfrequency resources and a periodicity of a discovery zone and toindicate operational parameters for the discovery zone, wherein theresources of the D2D discovery zone are allocated for D2D discoverysignal transmission by the ProSe-enabled UEs, wherein the signaling forthe D2D discovery zone configuration indicates one or more occurrencesof the discovery zone, and wherein the signaling is sent by the eNBeither using dedicated radio-resource control (RRC) signaling or sentusing common radio-resource control (RRC) signaling via systeminformation blocks (SIBs).
 30. The non-transitory computer-readablestorage medium of claim 29 wherein when the signaling sent by the eNBuses common RRC signaling via SIBs, the signaling sent by the eNBincludes at least one of a SIB transmission and a paging transmission,and wherein the discovery zone operational parameters include at leastone of a silencing factor, a transmit power control configuration,hopping related parameters and a scrambling ID.